Soil salinity is a common and serious environmental problem for plant growth in many parts of the world. Arbuscular mycorrhizal fungi (AMF) are thought of as bioameliorators that improve the soil salinity tolerance of plants. Stevia rebaudiana is broadly distributed in China, and is grown as a plant source of a new type of healthy alternative sweetener to sugar. However, few studies have been conducted to explore the role of AMF in the salinity tolerance of this plant. In this study, a greenhouse experiment was done with four treatment groups of this plant, composed of different combinations of salinity treatments (0 mmol/L and 200 mmol/L) and AMF treatments (inoculated with a sterilized AMF and with Glomus mosseae). The results showed that the treatment with the higher salinity significantly decreased the fresh weight, dry weight, substrate pH, and the percent of AMF structure in colonized root (m%) of S. rebaudiana, although salinity also significantly increased plant N and P concentrations. In the absence of salinity, AMF-inoculated plants had higher fresh and dry weights, while under salinity-stressed conditions the beneficial effects of the AMF were not evident (i.e. no difference from the non-inoculated plants was detected), which may have been due to significant decreases in the growth and activity of the AMF under severe salt stress. However, compared with the control plants AMF-inoculated plants had higher P concentrations, especially under saline conditions, and with increasing salinity the shoot mycorrhizal N response (MNR) significantly decreased while the shoot mycorrhizal P response (MPR) significantly increased. Obviously, the promotion of P accumulation by AMF colonization appears to be the mechanism underlying the increased salinity resistance of the AMF-inoculated plants. Therefore, it can be concluded that the accumulation of biomass in plants inoculated with G. mosseae will be promoted under non-saline conditions, while under saline conditions inoculated plants will acquire and accumulate more P. These findings provide theoretical guidance for the production and management of plants.